The combination of a film projector with a loop box for projecting intelligence recorded on a continuous loop of film is known in the art. See for example Griffith's U.S. Pat. No. 1,607,740 granted Nov. 23, 1926, Cornett U.S. Pat. No. 1,634,174 granted June 23, 1927 and Babb U.S. Pat. No. 2,101,126 granted Dec. 7, 1937.
Projection devices of the kinds illustrated in these prior art patents are primarily used for projecting a series of pictures and a message connected therewith. The message may either be printed as part of the film or be a separate sound track to give a verbal message accompanying the projection of the pictures on the film. It is customary for the projector to operate through one cycle and then stop until the operation of the apparatus is initiated for another cycle. The stopping and the starting is customarily controlled by the sprockets on the projection device at each side of a film gate, as those skilled in the art understand. The start up of the film loop from a resting position to a moving position places considerable stress on the film adjacent to the feed sprockets and it has been found by experience that there is a tendency to enlarge by tearing the sprocket holes in the film strip through which the teeth on the feed sprockets pass in order to have a positive drive of the film through the film gate. Such tearing soon makes the film loop unusable.
The Babb Patent recognizes that it is desirable to provide a device of this kind with a film feeding means that avoids or minimizes the development of this undesirable stress in the film and insures the proper functioning of the film feeding mechanism. See page 2, right column, lines 52 and following. Babb discloses means to accomplish this purpose including the sprocket wheels 33, 34 and 45 mounted on spindles which are driven at the same peripheral speed as the sprocket wheel forming part of the feeding mechanism 28 of the projector. See page 3, right column, lines 29 and following.